Laser Speckle Contrast Imaging

Laser Speckle Contrast Analysis (LASCA) is a method that visualizes tissue blood perfusion in the microcirculation instantaneously. It is an imaging technique that combines high resolution and speed.

When an object is illuminated by laser light, the backscattered light will form a random interference pattern consisting of dark and bright areas. This pattern is called a speckle pattern. If the illuminated object is static, the speckle pattern is stationary. When there is movement in the object, such as red blood cells in a tissue, the speckle pattern will change over time. In the PeriCam PSI System, a CCD camera will record these changes in the speckle pattern.

Static speckle pattern Moving speckle pattern

Depending on the degree of movement in the imaged area, the level of blurring will differ. The more movement there is in an image, the more blurred it will appear. The level of blurring is quantified by the speckle contrast. The contrast has been found to correlate with blood flow and this is how the LASCA technique can be implemented for blood perfusion measurements. The speckle contrast is defined as the ratio between the standard deviation of the intensity and the mean of the intensity. If there is a lot of movement, the blurring will increase and the standard deviation of the intensity will decrease, and consequently the speckle contrast will be lower. On the contrary, if there is no movement, the speckle contrast will be larger since the blurring will decrease and the standard deviation will increase. The mean intensity will remain unchanged.

The PeriCam PSI System records the blood perfusion using the arbitrary units, Perfusion Units (PU). In order to compare result accurately each instrument is factory calibrated. In addition, a Calibration Box is delivered with the PeriCam PSI System to allow for continuous control of calibration and adjustments.

PeriCam PSI

The PeriCam PSI is the latest generation laser speckle imager and comes in two versions, normal resolution (NR) with variable measurement area and high resolution (HR) with fixed focal distance.